Transcript Work of Gregor Mendel

Work of Gregor Mendel
Section 11-1
Pages 263-266
Standard IV Objective 2a: Explain Mendel’s laws of
segregation and independent assortment and their
role in genetic inheritance.
Genetics Vocabulary
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Trait: specific characteristic
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Gene: sequence of DNA that codes for a
protein thus determining a trait
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Alleles: different forms of a gene
Gregor Mendel
Gregor Mendel—father of genetics
 Conducted his work in the garden
of a monastery—changed biology forever
 Worked with true
breeding pea plants
 True breeding—produce
identical offspring if
allowed to self-pollinate
 He looked at 7 different
traits
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Alleles
Where do living organisms get alleles
from?
 Organisms receive one allele for each trait
from each parent.
 Principle of Dominance: some alleles are
dominant and other are recessive
 If a dominant allele is present, the
organism will take on the characteristic of
the dominant allele.
 PTC paper
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Alleles
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Representing different alleles
T (capital letter) = dominant trait
 t (lower case) = recessive trait
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For each trait there are two alleles (one
from each parent)
 Example: Plant height
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TT and Tt
 tt
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Probability
Principle of Probability: used to predict
outcomes of genetic crosses
 Homozygous – 2 identical alleles
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Homozygous dominant (TT)
 Homozygous recessive (tt)
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Heterozygous – 2 different alleles (Tt)
Mendel’s Crosses
Original pair of plants—P (parental)
generation
 The offspring of the P generation are
called the F1 generation
 The offspring of the F1 generation are
called the F2 generation
 Hybrid—the offspring of
crosses between parents
with different traits

Results of Crosses
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Mendel took the true breeding plants with
contrasting characteristics and crossed
them.
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Tall plant x Short plant
Took it another step: he allowed all hybrid
plants to produce an F2 generation by
self-pollination
Genetic Vocabulary
Heterozygous—organisms that have two
different alleles for the same trait
 Homozygous—organisms that have two
identical alleles for a particular trait
 Genotype—genetic makeup (TT, Tt, tt)
 Phenotype—physical characteristics (the
plant is tall or the plant is short)

Punnett Squares
Dad is heterozygous for a particular trait
 Mom is homozygous recessive for the
same trait
 What is the projected outcome of this
cross?
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Ratios
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Genotypic Ratio
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How many of each genotype do I have?
Do not reduce ratio!!!
H.D.:H.:H.R.
Ex. 1:2:1
Must add up to total number of boxes
Phenotypic Ratio
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How may of each phenotype do I have?
Is the plant tall or short?
Ex. 3:1
Picture Credits
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http://history.nih.gov/exhibits/nirenberg/images/photos/01_mendel_p
u.jpg
http://www.jbhs.k12.nf.ca/biology/photos/jillear2.jpg
http://sdmc.lit.org.sg/gedm/imageANDdata/gene.gif
http://www.naturalselectionreptiles.com/Genetics/allele.jpg
http://www.bbc.co.uk/schools/gcsebitesize/img/bipeas.gif
http://psychservices.ucsd.edu/resources_parents_web/resources_p
arents_images/resources_parents_help.jpg
http://images.google.com/imgres?imgurl=http://i21.photobucket.com/
albums/b268/plopperscioly/punnettsquare.jpg&imgrefurl=http://
http://stavos.homeip.net/detroitarchive/uploadcenter/images/tigon.jp
g
http://cricket.biol.sc.edu/herb/CC/Centrosema_virginianum2.jpg
http://users.adelphia.net/~lubehawk/BioHELP!/psquare0.jpg